Control method for optical fingerprint sensor and related control circuit

ABSTRACT

A control method for an optical fingerprint sensor and a touch controller are provided for canceling or reducing capacitive loading. The optical fingerprint sensor includes a plurality of pixels, and each of the pixels has a first control signal line and a second control signal line. Each of the pixels is further coupled to a first voltage source line, a second voltage source line and a sensing line. The control method includes the step of applying an anti-loading driving (ALD) signal on at least one of the first control signal line, the second control signal line, the first voltage source line, the second voltage source line and the sensing line when the touch controller is in a touch operation period.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S.application Ser. No. 16/907,176, filed on Jun. 20, 2020. U.S.application Ser. No. 16/907,176 is a continuation-in-part application ofU.S. application Ser. No. 15/086,073, filed on Mar. 31, 2016, whichclaims the benefit of U.S. Provisional Application No. 62/207,366, filedon Aug. 19, 2015. U.S. application Ser. No. 16/907,176 further claimsthe benefit of U.S. Provisional Application No. 62/878,291, filed onJul. 24, 2019, and U.S. Provisional Application No. 62/958,255, filed onJan. 7, 2020. The contents of these applications are incorporated hereinby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a control method for an opticalfingerprint sensor, and more particularly, to a control method for anoptical fingerprint sensor integrated with a touch panel.

2. Description of the Prior Art

Fingerprint recognition technology is widely applied in a variety ofelectronic products such as a mobile phone, laptop, tablet, personaldigital assistant (PDA), and portable electronics, for realizingidentity recognition. The fingerprint sensing allows a user to performidentity recognition conveniently, where the user may only need to puthis/her finger on a fingerprint sensing pad or area to login theelectronic device instead of entering long and tedious username andpassword.

Among those fingerprint sensing techniques, the optical fingerprintsensing scheme is commonly applied to an electronic product having adisplay panel. In general, the optical fingerprint sensing may beintegrated in a touch panel, so that both the fingerprint sensing andtouch sensing operations are feasible in the electronic device. However,the optical fingerprint sensing operation is required to be performedprecisely in order to capture tiny peak-to-valley differences of thefingerprint, and it is easily interfered with by the touch sensingoperation. Thus, there is a need for improvement over the prior art.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide acontrol method for an optical fingerprint sensor and the related controlcircuit and optical fingerprint sensor, in order to eliminate or reducethe interferences between the touch sensing operation and thefingerprint sensing operation.

An embodiment of the present invention discloses a control method for anoptical fingerprint sensor and a touch controller. The opticalfingerprint sensor comprises a plurality of pixels, and each of thepixels has a first control signal line and a second control signal line.Each of the pixels is further coupled to a first voltage source line, asecond voltage source line and a sensing line. The control methodcomprises the step of applying an anti-loading driving (ALD) signal onat least one of the first control signal line, the second control signalline, the first voltage source line, the second voltage source line andthe sensing line when the touch controller is in a touch operationperiod.

Another embodiment of the present invention discloses a control methodfor an optical fingerprint sensor and a touch controller. The opticalfingerprint sensor comprises a plurality of pixels, and each of thepixels has a first control signal line and a second control signal line.Each of the pixels is further coupled to a first voltage source line, asecond voltage source line and a sensing line. The control methodcomprises the step of configuring all of the first control signal line,the second control signal line, the first voltage source line, thesecond voltage source line and the sensing line to be floating when thetouch controller is in a touch operation period.

Another embodiment of the present invention discloses a control circuitfor controlling an optical fingerprint sensor. The optical fingerprintsensor comprises a plurality of pixels, and each of the pixels has afirst control signal line and a second control signal line. Each of thepixels is further coupled to a first voltage source line, a secondvoltage source line and a sensing line. The control circuit isintegrated with a touch controller to perform the step of applying anALD signal on at least one of the first control signal line, the secondcontrol signal line, the first voltage source line, the second voltagesource line and the sensing line when the touch controller is in a touchoperation period.

Another embodiment of the present invention discloses a control circuitfor controlling an optical fingerprint sensor. The optical fingerprintsensor comprises a plurality of pixels, and each of the pixels has afirst control signal line and a second control signal line. Each of thepixels is further coupled to a first voltage source line, a secondvoltage source line and a sensing line. The control circuit isintegrated with a touch controller to perform the step of configuringall of the first control signal line, the second control signal line,the first voltage source line, the second voltage source line and thesensing line to be floating when the touch controller is in a touchoperation period.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a display device according to anembodiment of the present invention.

FIG. 2 illustrates a 3-dimensional view of the display device shown inFIG. 1.

FIG. 3 illustrates a detailed structure of a fingerprint sensing pixelincluded in the fingerprint sensing layer shown in FIGS. 1 and 2.

FIG. 4 is a schematic diagram of deployment of the control signal lines,the sensing line and the voltage source lines in the fingerprint sensingpixel array.

FIG. 5A is a schematic diagram of applying the ALD signal to thefingerprint sensing pixel.

FIG. 5B illustrates a detailed implementation of applying the ALD signalto control the nodes to be floating.

FIG. 6 is a timing diagram of operations of a display device accordingto an embodiment of the present invention.

FIG. 7 illustrates a detailed implementation of the ALD signal during atouch operation period.

FIG. 8 is a schematic diagram of a display system according to anembodiment of the present invention.

FIG. 9 is a schematic diagram of another display system according to anembodiment of the present invention.

FIG. 10 is a schematic diagram of the ALD circuit according to anembodiment of the present invention.

FIGS. 11A and 11B are schematic diagrams of detailed implementations ofthe ALD generator.

FIG. 12 is a schematic diagram of another display system according to anembodiment of the present invention.

FIG. 13 is a schematic diagram of a process according to an embodimentof the present invention.

FIG. 14 is a schematic diagram of another process according to anembodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which is a schematic diagram of a display device10 according to an embodiment of the present invention. As shown in FIG.1, the display device 10 includes a display panel 100, and a row driver102 and a column sensor and driver 104. In this embodiment, the displaypanel 100 may be configured with touch sensing and fingerprint sensingfunctions; hence, a touch sensing layer 110 having a touch sensor arrayand a fingerprint sensing layer 120 having a fingerprint sensing pixelarray may be superposed on and integrated with the display panel 100.The row driver 102 and the column sensor and driver 104 form a controlcircuit for the fingerprint sensing pixel array. The display device 10may further include switch circuits 112_1 and 112_2, each of which maybe composed of multiplexers and/or switch circuits, for selectivelyforwarding the control signals to the target fingerprint sensing pixelsin the fingerprint sensing layer 120 or forwarding the sensing signalsfrom the fingerprint sensing pixels to a target receiver circuit in thecolumn sensor and driver 104. The display device 10 may further includecontrol circuits for display and touch sensing, which are omitted hereinfor brevity.

FIG. 2 illustrates a 3-dimensional view of the display device 10. Indetail, the touch sensing layer 110 includes a touch sensor array, wherethe touch sensor array has a plurality of sensing pads and a pluralityof conducting lines. A touch controller may send touch driving signalsto the sensing pads and correspondingly receive touch sensing signals todetermine a touch behavior. The touch driving signal may be a periodicsignal, which may have any type of pulses such as a sinusoidal wave,square wave, triangular wave or trapezoidal wave. Therefore, the touchsensing signal may also be a corresponding periodic signal carrying thetouch sensing information. The fingerprint sensing layer 120 includes afingerprint sensing pixel array, where each fingerprint sensing pixelmay include several circuit elements connected with row and columnconducting lines. The row conducting lines are connected to the rowdriver 102 and the column conducting lines are connected to the columnssensor and driver 104. These conducting lines may include severalcontrol signal lines configured to forward control signals, severalvoltage source lines configured to forward power voltages, and severalsensing lines configured to forward fingerprint sensing signals.

As shown in FIG. 2, the touch sensing layer 110 and the fingerprintsensing layer 120 are different layers but close to each other; hence,there is a non-ignorable coupling capacitor existing between eachconducting line of the touch sensing pad and each conducting line of thefingerprint sensing pixel. Therefore, if a touch driving signal is sentto the touch sensing pad, the coupling capacitor may couple the touchdriving signal or corresponding sensing signal to interfere with thevoltages on the control signal lines, the voltage source lines and/orthe sensing lines, to generate non-ignorable capacitive loading on thefingerprint sensing operations. From the perspective of the touchsensing operation, the coupling capacitor between the touch sensinglayer 110 and the fingerprint sensing layer 120 may also affect thesensing signal of the touch operation.

In this embodiment, the touch sensing layer 110 is the upper layersuperposed on the fingerprint sensing layer 120. In another embodiment,the fingerprint sensing layer may be the upper layer and the touchsensing layer may be the lower layer. Alternatively, the touch sensorand/or fingerprint sensor may be disposed in multiple layers. The panelstructure should not be a limitation to the scope of the presentinvention.

FIG. 3 illustrates a detailed structure of a fingerprint sensing pixelincluded in the fingerprint sensing layer 120 shown in FIGS. 1 and 2. Inthis embodiment, the fingerprint sensing pixel, which is configured torealize an optical fingerprint sensor, includes an optoelectronicelement PD, a storage capacitor SC and three transistors T1-T3. Thefingerprint sensing pixel may operate by receiving a first power voltagethrough a first voltage source line SVSS and a second power voltagethrough a second voltage source line SVDD. In an embodiment, the firstpower voltage may be a negative power voltage or a ground voltage or apositive power voltage, and the second power voltage may be a negativepower voltage or a ground voltage or a positive power voltage. Theactual polarity arrangement of the voltage source lines may bedetermined based on the circuit design of the sensing pixels, and thepresent invention is not limited herein. Three row control signals aresent to the pixel through control signal lines R_SW1-R_SW3,respectively, allowing the pixel to output a sensing signal through asensing line C_SEN. In another embodiment, the fingerprint sensingpixels are used to implement an optical fingerprint sensor, whichincludes an optoelectronic element PD, a storage capacitor SC and twotransistors T1-T2, making the circuit structure more simplified.

In the fingerprint sensing pixel, the optoelectronic element PD may be aphotodiode, which is configured to sense light and convert the sensedlight intensity into an electronic signal (such as a voltage signal orcurrent signal), and the operation is called “exposure”. During theexposure period, the electronic signal may flow into the storagecapacitor SC to be stored in the storage capacitor SC. The transistor T1may be served as a reset transistor, for resetting the voltage at thenode N2 (i.e., reset the electric charges stored in the storagecapacitor SC) before the exposure operation. The transistor T2 may beserved as a source follower, for forwarding the electronic signal sensedby the optoelectronic element PD and stored in the storage capacitor SCto the sensing line C_SEN after the exposure operation is complete. Thetransistor T3 may be served as a select transistor, which may be turnedon by the corresponding control signal when this pixel is selected.

As shown in FIG. 3, the transistor T1 has a gate terminal, a firstterminal and a second terminal, where the gate terminal is coupled tothe control signal line R_SW1 to receive a control signal such as areset signal, the first terminal is coupled to the first voltage sourceline SVSS, and the second terminal is coupled to the optoelectronicelement PD and the storage capacitor SC. Note that the first terminal ofthe transistor T1 may be one of the drain terminal and the sourceterminal and the second terminal of the transistor T1 may be the otherone, based on the current flow direction of the transistor T1. Each ofthe optoelectronic element PD and the storage capacitor SC has a firstterminal and a second terminal, where the first terminal is coupled tothe control signal line R_SW2 to receive a control signal such as a biasvoltage, and the second terminal is coupled to the second terminal ofthe transistor T1. The transistor T2 has a gate terminal, a firstterminal and a second terminal, where the gate terminal is coupled tothe second terminal of the transistor T1, the second terminal of theoptoelectronic element PD, and the second terminal of the storagecapacitor SC, the first terminal is coupled to the second voltage sourceline SVDD, and the second terminal is coupled to the transistor T3. Notethat the first terminal of the transistor T2 may be one of the drainterminal and the source terminal and the second terminal of thetransistor T2 may be the other one, based on the current flow directionof the transistor T2. The transistor T3 has a gate terminal, a firstterminal and a second terminal, where the gate terminal is coupled tothe control signal line R_SW3 to receive a control signal such as aselect signal, the first terminal is coupled to the second terminal ofthe transistor T2, and the second terminal is coupled to the sensingline C_SEN. Note that the first terminal of the transistor T3 may be oneof the drain terminal and the source terminal and the second terminal ofthe transistor T3 may be the other one, based on the current flowdirection of the transistor T3.

Please refer to FIG. 4, which is a schematic diagram of deployment ofthe control signal lines R_SW1-R_SW3, the sensing line C_SEN and thevoltage source lines SVSS and SVDD in the fingerprint sensing pixelarray. Considering FIG. 4 together with FIG. 1, each control signal lineR_SW1-R_SW3 may be coupled to a row of pixels, and each sensing lineC_SEN may be coupled to a column of pixels. Each voltage source lineSVSS or SVDD is coupled to the pixels through a connecting line in thecolumn direction. Therefore, the control signal lines R_SW1-R_SW3 may becoupled to the row driver 102, which is configured to send thecorresponding control signals. The sensing line C_SEN may be coupled tothe column sensor and driver 104, which is configured to receive thefingerprint sensing signals. Since the control signal lines R_SW1-R_SW3,the sensing line C_SEN, and the voltage source lines SVSS and SVDD arespread over the fingerprint sensing layer 120, all of these lines may beinterfered with by the touch driving/sensing signals applied to thetouch sensing layer 110.

According to the optical fingerprint sensing operations, the electronicsignal generated by the optoelectronic element PD is stored in thestorage capacitor SC; hence, it is preferable to prevent or reduce thecapacitive loading on both terminals of the storage capacitor SC, i.e.,the nodes N1 and N2, where the capacitive loading may be generated fromthe touch driving or sensing signal of the touch sensing pad. Forexample, if a coupling capacitor exists between the node N1 in thefingerprint sensing pixel and the touch sensing pad in the touch sensinglayer 110, the touch driving or sensing signal applied to the touchsensing pad may generate an interference to change the electronic signalstored in the storage capacitor SC, resulting in an error on thegenerated fingerprint sensing signal. In order to cancel or reduce thecapacitive loading, an anti-loading driving (ALD) signal may be appliedto the lines on the fingerprint sensing layer 120 or the lines may beconfigured to be floating when the touch driving signal is sent to thetouch sensing layer 110. When the touch controller is in a touchoperation period, at least one of the control signal lines R_SW1-R_SW3,the voltage source lines SVSS and SVDD, and the sensing line C_SEN isapplied with an ALD signal, and any other line not applied with the ALDsignal is configured to be floating. In another embodiment, when thetouch controller is in a touch operation period, all the control signallines R_SW1-R_SW3, the voltage source lines SVSS and SVDD, and thesensing line C_SEN may be configured to be floating. A signal line isfloating if a switch at the signal source is turned off or the signalsource outputs high impedance, and the present invention is not limitedherein. In short, by applying the ALD signals or making the signal linesfloating, or using various permutations and combinations of these twotechnical means, the interferences of signal coupling between the touchcontroller and the fingerprint sensor may be minimized.

Please refer to FIG. 5A, which is a schematic diagram of applying theALD signal to the fingerprint sensing pixel. In detail, a first ALDsignal may be applied on the control signal line R_SW2. Since thecontrol signal line R_SW2 is directly coupled to the node N1, the firstALD signal may be sent to the node N1 to cancel or reduce the capacitiveloading at the first terminal of the storage capacitor SC. In order tocancel or reduce the capacitive loading at the second terminal of thestorage capacitor SC, a second ALD signal may be sent to the node N2.Since the node N2 is coupled to the transistors T1 and T2, the secondALD signal may be applied on any one or more of the lines connected tothe transistor T1 and/or T2. These lines include, but not limited to,the control signal line R_SW1, the first voltage source line SVSS, thesecond voltage source line SVDD and the sensing line C_SEN. If thesecond ALD signal is applied on the control signal line R_SW1 and/or thefirst voltage source line SVSS, this second ALD signal may be coupled tothe node N2 through the parasitic capacitor(s) of the transistor T1. Ifthe second ALD signal is applied on the second voltage source line SVDDand/or the sensing line C_SEN, this second ALD signal may be coupled tothe node N2 through the parasitic capacitor(s) of the transistor T2.

Please note that the ALD signals aim at canceling or reducing thecapacitive loading of the fingerprint sensing pixel. Preferably, an ALDsignal may be exactly identical to the touch driving signal sent to thetouch sensing pad, as shown in FIG. 5A. The touch driving signal mayinterfere with the fingerprint sensing pixel through capacitive couplingof the coupling capacitors CC1 and CC2. Without the ALD signal, when thetouch driving signal toggles, the voltage variation of the touch drivingsignal may cause the coupling capacitors CC1 and CC2 to perform chargingor discharging, resulting in an unpredictable voltage variation on thenode N1 and/or N2. If the ALD signals exactly identical to the touchdriving signal are applied to the nodes N1 and N2 while the touchdriving signal toggles, the cross voltages of the coupling capacitorsCC1 and CC2 may keep constant, which means that the coupling capacitorsCC1 and CC2 may not perform charging or discharging, and thus may notinfluence the electronic signal stored in the storage capacitor SC.

As mentioned above, the touch driving signal may be a periodic signalhaving a plurality of pulses. Therefore, the ALD signal may also be amodulation signal with multiple pulses where the frequency, phase, andamplitude of the pulses are substantially identical to the frequency,phase, and amplitude of the pulses of the touch driving signal. Sincethe touch driving signal may have any type of pulses such as sinusoidalwave, square wave, triangular wave or trapezoidal wave, the ALD signalmay be modulated to have the same or similar type of pulses.

Please note that an ALD signal may be or may not be exactly the same asthe touch signal such as the touch driving signal or touch sensingsignal. For example, in an embodiment, the amplitude of the ALD signalmay be slightly smaller than the amplitude of the touch driving signal,while their frequencies and phases are substantially identical.Alternatively or additionally, the phase of the ALD signal may have asmall shift from the phase of the touch driving signal, while theirfrequencies are substantially identical. The higher similarity betweenthe ALD signal and the touch signal may generate higher performance ofreducing the capacitive loading of the fingerprint sensing pixel.

The ALD signals may be applied on the lines of the fingerprint sensingpixel in any manner. In an embodiment, an ALD signal may be applied to atarget line by driving the target line with the ALD signal, where theALD signal may be substantially identical to the touch signal (withidentical frequency, phase and/or amplitude). Alternatively oradditionally, an ALD signal may be applied to a switch of a target lineto control the corresponding node to be floating. In thisimplementation, the ALD signal may have any possible pattern. Forexample, the ALD signal may be a periodic signal having any type ofpulses as described above, or may be a signal in an appropriate voltagelevel that may turn off the corresponding switch. As long as the switchmay be turned off by the ALD signal to let the target node to befloating for a period of time, this ALD operation may be feasible. Thefloating status allows the voltage of the target node to shift upward ordownward following the pulses in the touch signal due to the couplingcapacitor CC1 or CC2. A node may be floating when every terminal of thisnode is only connected to high impedance node(s), or any externalconnection of this node is cut off; that is, all switches connected tothe node are turned off. The floating operation may be applied for thesake of power saving or if it is not feasible to drive the target linewith a signal. The target line that receives the ALD signal may be thecontrol signal line R_SW2 coupled to the node N1, and/or any otherpossible lines coupled to the pixel, such as the control signal linesR_SW1 and R_SW3, the first voltage source line SVSS, the second voltagesource line SVDD and the sensing line C_SEN.

FIG. 5B illustrates a detailed implementation of applying the ALD signalto control the nodes to be floating. The pixel structure shown in FIG.5B is similar to the pixel structure shown in FIG. 5A, so signals andelements having similar functions are denoted by the same symbols. Thestructure of FIG. 5B further includes switches PSW1-PSW5 respectivelycoupled to the control signal line R_SW2, the control signal line R_SW1,the first voltage source line SVSS, the second voltage source line SVDDand the sensing line C_SEN. Note that each of the switches PSW1-PSW5 maybe a switch dedicated to the target pixel, or may be a switch of thetarget line for connecting to a row or column of pixels. In anotherembodiment, the signal line is configured to be in a floating status byturning off the switch at the signal source or making the signal sourceoutput high impedance, or all the above signal lines may be connectedtogether and controlled by a master switch. The present invention is notlimited thereto.

In detail, in order to apply the ALD signal to the fingerprint sensingpixel, a first ALD signal may be applied to the switch PSW1. In such asituation, the switch PSW1 coupled between the node N1 and the controlsignal line R_SW2 may be turned off, so as to control the node N1 to befloating. Further, in order to control the node N2 to be floating, asecond ALD signal may be applied to any one or more of the switch PSW2coupled to the control signal line R_SW1, the switch PSW3 coupled to thefirst voltage source line SVSS, the switch PSW4 coupled to the secondvoltage source line SVDD, and the switch PSW5 coupled to the sensingline C_SEN. In such a situation, any nodes of the pixel coupled to thecontrol signal line R_SW1, the first voltage source line SVSS, thesecond voltage source line SVDD and the sensing line C_SEN may befloating, and thus the node N2 may be floating.

As for the fingerprint sensing pixel array in the fingerprint sensinglayer 120, the ALD signals may be implemented flexibly by applying themethods of driving with the ALD signal and/or controlling the node to befloating to each pixel. For example, the lines of a first pixel may bedriven with an ALD signal while the lines of a second pixel may becontrolled by the ALD signal to let the corresponding node(s) to befloating. The ALD signals for a fingerprint sensing pixel array with 2columns (Col1 and Col2) and 2 rows (Row1 and Row2) may have variousimplementations described as Table 1, as shown below:

TABLE 1 Touch Fingerprint sensing pixel Case element Row1 Row2 Col1 Col21 Driving Driving Driving Driving Driving 2 Driving Driving FloatingFloating Floating 3 Driving Floating Driving Floating Floating 4 DrivingFloating Floating Driving Floating 5 Driving Floating Floating FloatingDriving 6 Driving Driving Driving Floating Floating 7 Driving DrivingFloating Driving Floating 8 Driving Driving Floating Floating Driving 9Driving Floating Driving Driving Floating 10 Driving Floating DrivingFloating Driving 11 Driving Floating Floating Driving Driving 12 DrivingDriving Driving Driving Floating 13 Driving Driving Driving FloatingDriving 14 Driving Driving Floating Driving Driving 15 Driving FloatingDriving Driving Driving 16 Driving Floating Floating Floating Floating

According to Table 1, there may be at least 16 different implementationsof the ALD signals for the pixel array, and the ALD signals may beapplied when the touch driving signal is sent to the touch element. Notethat a general fingerprint sensing pixel array may include more than 2rows and 2 columns of pixels, and thus more combinations of driving andfloating operations may be feasible. In an embodiment, the ALD signalsfor different lines connected to the same row of pixels and/or differentlines connected to the same column of pixels may further be implementedin different manners, so as to realize the flexibility of ALDoperations.

Please refer to FIG. 6, which is a timing diagram of operations of adisplay device according to an embodiment of the present invention. Inorder to reduce the interferences between display, touch sensing, andfingerprint sensing operations, these operations may be performed basedon time division. As shown in FIG. 6, the touch operation period (TP)and the display period (DP) may be configured alternately in the displaytime for each frame, and the fingerprint sensing period (FP) may beconfigured in the blank time between two consecutive display frames.Considering FIG. 6 together with FIG. 3, the operations of opticalfingerprint sensor require that the node N2 is reset to a predeterminedvoltage level, then exposure starts, and then the electronic signalgenerated in the exposure procedure is read out at the end of theexposure period. In general, the exposure period may persist for a frameof display cycle including several display periods and touch operationperiods, as shown in FIG. 6. In another embodiment, the exposure periodmay cross several display frames in order to generate enough sensingsignals.

During the exposure period, the electronic signals of the optoelectronicelement PD may continuously be generated and accumulated in the storagecapacitor SC, and the voltage on the node N2 may change correspondingly.Therefore, the ALD signal may be applied during the exposure period, inorder to prevent the electric charges stored in the storage capacitor SC(i.e., the voltage across the storage capacitor SC) from beinginterfered with by the touch signals before the fingerprint sensingsignal is read out.

More specifically, the touch operation may be performed during the touchoperation periods; that is, the touch driving signals may usually togglein the touch operation periods. Therefore, the ALD signal may be appliedduring the touch operation periods. FIG. 7 illustrates a detailedimplementation of the ALD signal during a touch operation period. Asshown in FIG. 7, a touch sensing line may receive a touch signal from asensing pad during the touch operation period, the touch signal havingsquare-wave pulses with an amplitude equal to ΔV. Therefore, the ALDoperation may be applied to the fingerprint sensing pixels during thetouch operation period.

In this embodiment, the first voltage source line SVSS and the secondvoltage source line SVDD may forward a power voltage during thefingerprint sensing period and the display period, and forward the ALDsignal during the touch operation period, where the ALD signal mayinclude multiple pulses generated by modulating the power voltage, andthe pulses have substantially identical frequency, phase and amplitudeas the touch signal applied to the touch sensing line. The controlsignal lines R_SW1-R_SW3 may forward corresponding control signalsduring the fingerprint sensing period and the display period, andforward the ALD signal during the touch operation period, where the ALDsignal may include multiple pulses generated by modulating the controlsignals, and the pulses have substantially identical frequency, phaseand amplitude as the touch signal applied to the touch sensing line. Thesensing line C_SEN may forward the sensing signal during the fingerprintsensing period, and forward the ALD signal during the touch operationperiod, where the ALD signal may include multiple pulses, and the pulseshave substantially identical frequency, phase and amplitude as the touchsignal applied to the touch sensing line.

Please refer to FIG. 8, which is a schematic diagram of a display system80 according to an embodiment of the present invention. As shown in FIG.8, the display system 80 includes a system processor (AP) 800, afingerprint, touch and display integration (FTDI) circuit 802 and adisplay panel 804, where the FTDI circuit 802 may be a single chipintegrated with processing circuits for display, touch and fingerprintsensing operations. In detail, the system processor 800 may be a coreprocessor of the display system 80, such as a central processing unit(CPU), a microcontroller unit (MCU), a microprocessor, or the like. Asfor a smart phone, the system processor 800 may be an MCU configured tocontrol various applications and operations of the smart phone. Notethat the algorithm for fingerprint recognition is usually quite complex,such that fingerprint matching and determination should be performed inthe system processor 800 having larger computation resources and may notbe realized in the FTDI circuit 802. The FTDI circuit 802 aims atcapturing or extracting the fingerprint image received from the displaypanel 804, and processing the received fingerprint sensing signals toamplify and acquire the desired peak-to-valley data.

The display panel 804 may be the display panel 100 shown in FIG. 1,where the touch sensing layer 110 and the fingerprint sensing layer 120are included, for realizing the three-in-one integration of display,touch and fingerprint sensing operations. The FTDI circuit 802 may beserved as a control circuit for controlling the display, touch andfingerprint sensing operations of the display panel 804. In anembodiment, the display panel 804 may be an in-cell touch andfingerprint panel, where the touch sensor and fingerprint sensor andtheir related connecting lines are disposed inside the display panel804; hence, the distance between the touch sensing layer 110 and thefingerprint sensing layer 120 may be quite near, and thus the couplingcapacitors between the touch sensing layer 110 and the fingerprintsensing layer 120 may generate severe loading on the fingerprint sensingoperation.

As shown in FIG. 8, a fingerprint (FPR) control circuit 820, a touchcontroller 822 and a display driver 824 may be integrated in the FTDIcircuit 802, and each of these modules communicates with the systemprocessor 800 through a specific interface. The FTDI circuit 802 mayfurther include an ALD circuit 850, which may be selectively implementedin the touch controller 822 or the fingerprint control circuit 820 (asan example shown in FIG. 8, the ALD circuit 850 is implemented in thefingerprint control circuit 820). The fingerprint control circuit 820,which may include a row driver (and/or sensor) and a column driver(and/or sensor) as shown in FIG. 1, may send control signals to controlthe fingerprint sensing pixels in the display panel 804, allowing thepixels to send fingerprint sensing signals in a specific sequence. Thefingerprint control circuit 820 may also include a readout circuitconfigured to receive the sensing signals from each fingerprint sensingpixel. The touch controller 822 is configured to send touch drivingsignals to the touch sensing pad in the touch sensing layer of thedisplay panel 804 and correspondingly receive touch sensing signals. Thedisplay driver 824 is configured to perform display control of thedisplay panel 804. Specifically, the display driver 824 may receiveimage data from the system processor 800, and correspondingly generateand output image signals to the display panel 804.

In order to realize the ALD operation, in the touch operation periodand/or the exposure period, the ALD circuit 850 of the FTDI circuit 802may further be configured to drive the line(s) of the fingerprintsensing pixel with the ALD signal, or control the corresponding node(s)of the fingerprint sensing pixel to be floating. In an embodiment, theALD circuit 850 implemented in the fingerprint control circuit 820 mayapply the ALD signal according to a notification received from the touchcontroller 822, allowing the ALD signal to be synchronized with thetouch signal, so that the ALD signal and the touch signal may beconfigured to have identical frequency and phase, and/or amplitude. Thenotification may be in any form such as a flag, a voltage level, or atoggle in a connecting line between the fingerprint control circuit 820and the touch controller 822.

In addition to the fingerprint control circuit 820, the display driver824 may also apply an ALD signal on the display circuits of the displaypanel 804 during the touch operation period. This may prevent or reducethe capacitive loading of the display circuits caused by the couplingcapacitors between the display pixels and the touch sensing layer.

Please note that the implementation of the FTDI circuit 802 shown inFIG. 8 is one of various embodiments of the present invention. Inanother embodiment, the circuitry for controlling the display panel maybe implemented in a 2-chip scheme. Please refer to FIG. 9, which is aschematic diagram of another display system 90 according to anembodiment of the present invention. The circuit structure of thedisplay system 90 is similar to the circuit structure of the displaysystem 80, so signals and elements having similar functions are denotedby the same symbols. As shown in FIG. 9, the display system 90 isdifferent from the display system 80 in that, the display system 90includes a touch and display driving integration (TDDI) circuit 902 anda fingerprint readout circuit (FPR ROIC) 903, which replace thefunctions of the FTDI circuit 802 in the display system 80. The FPR ROIC903 may have an ALD circuit 950. The FPR ROIC 903 is configured to readout fingerprint sensing signals from the fingerprint sensing pixels, andalso configured to apply the ALD signals to the lines of the fingerprintsensing pixels by the ALD circuit 950. Each of the TDDI circuit 902 andthe FPR ROIC 903 may be implemented as the integrated circuit in a chip,and these two chips cooperate to control the display, touch sensing andfingerprint sensing operations of the display panel 804. An interface isdisposed between the TDDI circuit 902 and the FPR ROIC 903, forforwarding necessary messages such as the notification for applying theALD signal and the information for synchronizing the display driving,touch sensing and fingerprint sensing operations. The detailedoperations of the display system 90 are similar to the operations of thedisplay system 80 as described above, and will be omitted herein forbrevity.

The ALD circuit of the FTDI circuit 802 or the FPR ROIC 903 may beimplemented in any possible manners. Please refer to FIG. 10, which is aschematic diagram of an ALD circuit 1000 according to an embodiment ofthe present invention. As shown in FIG. 10, the ALD circuit 1000includes a voltage generator 1002, an ALD generator 1004 and a couplingcapacitor CC. The voltage generator 1002 is configured to generate avoltage VH. The voltage VH may be any possible voltage such as a controlvoltage for the control signal line or a power voltage for the voltagesource line. The ALD generator 1004 is configured to generate anoriginal ALD signal ALDX. The original ALD signal ALDX may be a periodicsignal having any type of pulses such as a sinusoidal wave, square wave,triangular wave or trapezoidal wave. The original ALD signal ALDX may becoupled to the output terminal of the ALD circuit 1000 through thecoupling capacitor CC, to be carried on the level of the voltage VH andoutputted by the ALD circuit 1000, as shown in FIG. 10.

FIG. 11A illustrates a detailed implementation of the ALD generator1004. As shown in FIG. 11A, the ALD generator 1004 includes voltageregulators 1102 and 1104, capacitors C1 and C2 and a switch module 1110.The voltage regulator 1102 is configured to generate and output avoltage V1 and the voltage regulator 1104 is configured to generate andoutput a voltage V2, where the value of the voltage V1 may be higherthan the value of the voltage V2 with an appropriate difference. Thecapacitors C1 and C2, respectively coupled to the output terminal of thevoltage regulators 1102 and 1104, may be served to improve the stabilityof the voltages V1 and V2. The switch module 1110 may receive thevoltages V1 and V2, and alternately output the voltages V1 and V2 withappropriate control of the switches, in order to generate the originalALD signal ALDX. In this implementation, the original ALD signal ALDXmay be a square-wave signal switched between the levels of the voltagesV1 and V2.

FIG. 11B illustrates another implementation of the ALD generator 1004.As shown in FIG. 11B, the ALD generator 1004 includes adigital-to-analog converter (DAC) 1150. The DAC 1150 may receive aseries of digital codes DIG, and correspondingly generate and output theoriginal ALD signal ALDX by converting the digital codes DIG into analogvoltages. In this implementation, the original ALD signal ALDX may haveany possible waveform based on the received digital codes DIG.

As mentioned above, the ALD circuit may be included in the FTDI circuit802 as shown in FIG. 8 or may be included in the FPR ROIC 903 as shownin FIG. 9. In another embodiment, an ALD circuit may be implemented inthe fingerprint sensor of the display panel. Please refer to FIG. 12,which is a schematic diagram of another display system 1200 according toan embodiment of the present invention. The circuit structure of thedisplay system 1200 is similar to the circuit structure of the displaysystem 80, so signals and elements having similar functions are denotedby the same symbols. As shown in FIG. 12, the display system 1200 isdifferent from the display system 80 in that, in the display system1200, the ALD circuit 1250 is implemented in the fingerprint sensor ofthe display panel 804. The ALD circuit 1250 may be coupled to thefingerprint sensing pixel array, and perform its operation by receivinga control signal CTRL from the FTDI circuit 802. For example, the ALDcircuit 1250 may have a structure similar to the ALD circuit 1000 shownin FIG. 10, where the ALD generator 1004 may output the original ALDsignal ALDX when it is enabled or triggered by the control signal CTRL.Alternatively, the control signal CTRL may be the original ALD signalALDX, which is configured to drive the ALD circuit 1250 to output theALD signal on an intended voltage level.

In another embodiment, the configurations of including the ALD circuitin the fingerprint sensor may also be combined with the 2-chip structurehaving a fingerprint readout circuit and a TDDI circuit as shown in FIG.9. The related operations of this implementation are similar to thosedescribed above, and will not be narrated herein.

It should also be noted that the embodiments of the present inventionaim at providing a control method for an optical fingerprint sensor anda related control circuit and optical fingerprint sensor. Those skilledin the art may make modifications and alternations accordingly. It iswell known that there are various types of pixel structures in thefingerprint sensing layer of the display panel, and the pixel structuredescribed in this disclosure is one of various implementations of thefingerprint sensing pixel. For example, an additional switch may bedisposed between the optoelectronic element and the storage capacitor,so that the exposure time may be controlled by operating the switch. Insuch a situation, the ALD signal(s) may be applied based on thestructure of the fingerprint sensing pixel.

In addition, the deployment of row (horizontal) control signal lines,column (vertical) sensing lines and column (vertical) voltage sourcelines shown in FIG. 4 is one of various embodiments of the presentinvention. In another embodiment, the sensing lines and the voltagesource lines may be disposed along the horizontal direction, and thecontrol signal lines may be disposed along the vertical direction; orseveral of the control signal lines may be disposed along the horizontaldirection and other control signals may be disposed along the verticaldirection. The row/column control circuits for the fingerprint sensingpixels may be disposed correspondingly. For example, if the sensinglines are row sensing lines disposed along the horizontal direction, therow control circuit may include a sensor module capable of receiving thesensing signals. The deployments of these lines and the control circuitsmay not be a limitation to the scope of the present invention.

Further, the method of applying the ALD signal(s) to the fingerprintsensing pixels may be applied to any type of display panel which isintegrated with touch and fingerprint sensing functions, such as aliquid crystal display (LCD) panel, an organic light-emitting diode(OLED) panel, or a plasma display panel (PDP). As for the LCD panel, theALD operations are applicable in an in-cell, on-cell or out-cell LCDpanel. Note that it is more preferable to apply the ALD signal in anin-cell touch panel with fingerprint sensing functions, since the touchsensing layer is much closer to the fingerprint sensing layer under thein-cell structure, but the implementations should not be limitedthereto.

The abovementioned operations of the optical fingerprint sensor and thefingerprint control circuit may be summarized into a process 1300, asshown in FIG. 13. The process 1300, which may be realized in thefingerprint control circuit or the ALD circuit, may be performed on theoptical fingerprint sensor integrated with a touch controller and havinga plurality of fingerprint sensing pixels, where each pixel may includea first control signal line and a second control signal line, and may becoupled to a first voltage source line, a second voltage source line anda sensing line, as the pixel structure shown in FIG. 3. As shown in FIG.13, the process 1300 includes the following steps:

Step 1302: Start.

Step 1304: Apply an ALD signal on at least one of the first controlsignal line, the second control signal line, the first voltage sourceline, the second voltage source line and the sensing line when the touchcontroller is in a touch operation period.

Step 1306: End.

Note that those lines among the first control signal line, the secondcontrol signal line, the first voltage source line, the second voltagesource line and the sensing line not applied with the ALD signal may becontrolled to be floating. Further, the fingerprint control circuit mayalso adopt a control method mainly based on floating, as the process1400 shown in FIG. 14, where the process 1400 includes the followingsteps:

Step 1402: Start.

Step 1404: Configure all of the first control signal line, the secondcontrol signal line, the first voltage source line, the second voltagesource line and the sensing line to be floating when the touchcontroller is in a touch operation period.

Step 1406: End.

The detailed implementations and alternations of the processes 1300 and1400 are illustrated in the above paragraphs, and will not be narratedherein.

To sum up, the embodiments of the present invention provide a controlmethod for an optical fingerprint sensor and the related control circuitand optical fingerprint sensor. The optical fingerprint sensor may beintegrated with a touch panel, where one of the touch sensing layer andthe fingerprint sensing layer may be superposed on and close to theother one, resulting in large capacitive loading due to the couplingcapacitors between the touch sensing layer and the fingerprint sensinglayer. During the touch operation period, the touch signal may generatecapacitive loading on the lines of the fingerprint sensing pixels. Inorder to eliminate or reduce the capacitive loading, an ALD signal maybe applied on the lines of the fingerprint sensing pixels. The ALDsignal may be applied to drive the line(s), where the ALD signal has afrequency, phase, and/or amplitude substantially identical to thefrequency, phase, and/or amplitude of the touch signal, respectively.Alternatively or additionally, the ALD operation may be realized bycontrolling the target node(s) of the fingerprint sensing pixels to befloating. The ALD operation may be performed during the touch operationperiod of the touch controller and/or the exposure period of the opticalfingerprint sensor. The lines of a fingerprint sensing pixel receivingthe ALD signal may include the line directly coupled to the storagecapacitor of the pixel and the line coupled to the storage capacitorthrough a transistor. With the ALD operation, the voltages at bothterminals of the storage capacitor may not be interfered with by thetouch signals, so as to maintain the accuracy of fingerprint sensingsignals.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A control method for an optical fingerprintsensor and a touch controller, the optical fingerprint sensor comprisinga plurality of pixels, each of the pixels having a first control signalline and a second control signal line, each of the pixels furthercoupled to a first voltage source line, a second voltage source line anda sensing line, the control method comprising: applying an anti-loadingdriving (ALD) signal on at least one of the first control signal line,the second control signal line, the first voltage source line, thesecond voltage source line and the sensing line when the touchcontroller is in a touch operation period.
 2. The control method ofclaim 1, wherein the ALD signal is applied during an exposure period ofthe optical fingerprint sensor.
 3. The control method of claim 1,wherein any line among the first control signal line, the second controlsignal line, the first voltage source line, the second voltage sourceline and the sensing line not applied with the ALD signal is configuredto be floating.
 4. The control method of claim 1, wherein a controlcircuit of the optical fingerprint sensor and the touch controller areintegrated with a display driver, and the ALD signal comprises a pulsehaving a frequency and a phase substantially identical to a frequencyand a phase of a touch signal of the touch controller, respectively. 5.The control method of claim 4, wherein an amplitude of the ALD signal issubstantially identical to an amplitude of the touch signal.
 6. Acontrol method for an optical fingerprint sensor and a touch controller,the optical fingerprint sensor comprising a plurality of pixels, each ofthe pixels having a first control signal line and a second controlsignal line, each of the pixels further coupled to a first voltagesource line, a second voltage source line and a sensing line, thecontrol method comprising: configuring all of the first control signalline, the second control signal line, the first voltage source line, thesecond voltage source line and the sensing line to be floating when thetouch controller is in a touch operation period.
 7. A control circuitfor controlling an optical fingerprint sensor, the optical fingerprintsensor comprising a plurality of pixels, each of the pixels having afirst control signal line and a second control signal line, each of thepixels further coupled to a first voltage source line, a second voltagesource line and a sensing line, the control circuit being integratedwith a touch controller to perform the following step: applying ananti-loading driving (ALD) signal on at least one of the first controlsignal line, the second control signal line, the first voltage sourceline, the second voltage source line and the sensing line when the touchcontroller is in a touch operation period.
 8. The control circuit ofclaim 7, wherein the control circuit is configured to apply the ALDsignal during an exposure period of the optical fingerprint sensor. 9.The control circuit of claim 7, wherein any line among the first controlsignal line, the second control signal line, the first voltage sourceline, the second voltage source line and the sensing line not appliedwith the ALD signal is configured to be floating.
 10. The controlcircuit of claim 7, wherein the second control signal line is coupled toa first terminal of a storage capacitor of the corresponding pixel amongthe plurality of pixels.
 11. The control circuit of claim 10, wherein asecond terminal of the storage capacitor is coupled to a firsttransistor and a second transistor of the corresponding pixel.
 12. Thecontrol circuit of claim 11, wherein the first transistor is furthercoupled to the first control signal line and the first voltage sourceline.
 13. The control circuit of claim 11, wherein the second transistoris further coupled to the second voltage source line.
 14. The controlcircuit of claim 11, wherein the second transistor is further coupled tothe sensing line through a third transistor.
 15. The control circuit ofclaim 10, wherein the storage capacitor is coupled to an optoelectronicelement.
 16. The control circuit of claim 7, wherein the opticalfingerprint sensor is in an exposure period.
 17. The control circuit ofclaim 7, wherein the control circuit, the touch controller and a displaydriver are integrated with each other, and the ALD signal comprises apulse having a frequency and a phase substantially identical to afrequency and a phase of a touch signal of the touch controller,respectively.
 18. The control circuit of claim 17, wherein an amplitudeof the ALD signal is substantially identical to an amplitude of thetouch signal.
 19. The control circuit of claim 7, wherein the controlcircuit is integrated with the touch controller, and the control circuitis configured to apply the ALD signal according to a notificationreceived from the touch controller.
 20. A control circuit forcontrolling an optical fingerprint sensor, the optical fingerprintsensor comprising a plurality of pixels, each of the pixels having afirst control signal line and a second control signal line, each of thepixels further coupled to a first voltage source line, a second voltagesource line and a sensing line, the control circuit being integratedwith a touch controller to perform the following step: configuring allof the first control signal line, the second control signal line, thefirst voltage source line, the second voltage source line and thesensing line to be floating when the touch controller is in a touchoperation period.